1. Field of the Invention
The present invention relates to a coating material comprising a crosslinker component and a catalyst component, the coating material curing at temperatures of just 10 to 80° C., to the use of the coating materials and to coating compositions comprising them.
2. Description of the Background
For the permanently protective coating of heat-sensitive substrates it is nowadays common to use two-component paints which are able to cure just at ambient temperature. They consist of film-forming resins having functional groups and of crosslinkers which react just at ambient temperature with these functional groups, with crosslinking taking place. On account of their high reactivity, these crosslinkers frequently possess an intrinsic toxicological hazard potential to humans. There is, therefore, a desire to provide alternative coating systems which possess a comparably broad application spectrum, in conjunction with a high level of resistance on the part of the cured coatings towards effects of chemicals or of weathering, and also towards mechanical exposure. The technical benchmark to be employed is the long-established aliphatic 2K (2-component) PU systems.
One possible alternative is represented by coating systems based on organofunctional silanes, which have proved to be highly performing after heat curing and so are already being used for automotive OEM finishing.
Described in EP-549 643, WO 92/11327, WO 92/11328 and U.S. Pat. No. 5,225,248 is the use of resins containing silane groups in non-aqueous, heat-curing clearcoats for automotive OEM finishing, where, usually, curing temperatures upwards of 120° C. are employed. Since the reactivity profile requirements imposed in automotive finishing are fundamentally different from those in the case of ambient temperature drying, the catalysts specified there, and their concentrations, are unsuitable for curing at below 80° C.
Partially silanized polyisocyanates for scratch-resistant clearcoats are known from EP-A 1273640. They are required to possess free NCO groups in order for curing to take place with sufficient rapidity. Furthermore, the crosslinkers described therein are used in heat-curing coatings for automotive finishing—that is, curing temperatures of more than 120° C. are employed. The claimed use of blocked sulfonic acid catalysts which develop their activity only at above 100° C. is therefore unsuitable for curing at temperatures below 80° C.
Described in the technical literature are a variety of catalysis principles for accelerating the curing of silane-containing reactive systems.
DE 102004050747 A1 discloses catalysts of the Lewis acid type. Used accordingly as catalysts for the crosslinking of the silane functionalities are Lewis acids (electron-deficient compounds), such as tin naphthenate, tin benzoate, tin octoate, tin butyrate, dibutyltin dilaurate, dibutyltin diacetate, dibutyltin oxide, and lead octoate, for example. Catalysts used here are also, preferably, metal complexes with chelate ligands. The compounds which form chelate ligands are organic compounds having at least two functional groups that are able to coordinate to metal atoms or metal ions. These functional groups are usually electron donors which give up electrons to metal atoms or metal ions. On account of their heavy metal character, these catalysts are frequently objectionable toxicologically and more particularly in any case are not sufficiently active to ensure rapid curing at ambient temperature.
Lewis acid types or else sulfonic or phosphoric acid catalysts are the catalysts usually described and utilized in silane technology.
In experiments, however, it has emerged that the catalysts described above are not suitable for ambient temperature curing.
EP 1 624 027 describes combinations of metal carboxylates or organic carboxylic acids and heteroatom-containing silanes for catalysing the curing of dimethoxysilane-based sealants. In that case, however, liquid carboxylic acids which have a low viscosity and a particularly preferred melting point of −40 to +35° C. are claimed and in all of the examples are combined with amines—that is, they are used in neutralized form. The extent to which this principle can be transposed from highly elastic sealants to highly crosslinked coating systems is not disclosed and is not apparent to the skilled person.
U.S. Pat. No. 4,863,520 describes the use of tetralkylammonium carboxylates in sol-gel systems based on reaction products of colloidal silicas, alkyltrialkoxysilanes and water. In this reference, however, tetralkylammonium carboxylates are used for condensing the silanol groups which have formed through the hydrolysis of the silanes. These systems are cured preferably at temperatures above 80° C., preferably above 100° C. Curing at lower temperatures is not disclosed.